New phosphorous-containing polyesters were prepared by polycondensation of 2-(6-oxido-6H-dibenz < c,e >< 1,2 > oxaphosphorin-6-yl)-1,4-naphthalene diol, 1, with different aromatic dicarboxylic acids using a SOCl2/pyridine condensing agent. Two poly(ester-imide)s were prepared by polycondensation in solution at high temperature of the same aromatic bisphenol 1, with diacid chlorides containing preformed imide rings. The most of the polymers were easily soluble in polar organic solvents such as N-methylpyrrolidone, N,N-dimethylformamide and chloroform. They showed high thermal stability, the decomposition temperature being in the range of 330-442 degrees C and glass transition in the temperature range of 193-226 degrees C. One of these polymers exhibited thermotropic liquid crystalline behavior. Due to the presence of phosphorus the polymers gave high char yield in termogravimetric analysis, hence good name retardant properties.